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Old 03-19-2018, 11:25 PM
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Default Motors for a BIG boat?

As the title says, I'm working on a very large RC boat. A 16' catamaran, that should weigh around 400 pounds. Right now I'm looking at propulsion, and have some questions about RC motors I was hoping somebody could help me with.

If I've done my math correctly, then to push my boat at ~10 mph top speed then I need to spin a pair of ~6"x6" props at ~3000 RPM, which should take ~5 HP. My power is coming from a pair of very large deep cycle batteries, so nominal voltage is only 24V. So, a 125 kv motor that can produce ~1500W of power at 24V should do the trick, right?

Motors marketed for RC boats seem to mostly be aimed at much higher RPM, so I've been looking at plane motors, and it looks like something like the Turnigy Aerodrive SK3 149kv is pretty close (can't post a link, sorry).

149kv should produce around 3500 RPM on 24V. Giving it 24V of the expected 44V should result in ~55% max power, for around 1,250W, right?

Am I completely off in my math, here? Or, better yet, does somebody have a recommendation for a pair of motors that could meet my requirements?